Clinical and laboratory studies are conducted to determine etiology (infection, immunity and/or genetics) of chronic diseases of the peripheral and central nervous system. Current studies include amyotrophic lateral sclerosis, (ALS), polymyositis/dermatomyositis, new post-polio muscle weakness, demyelinating polyneuropathies, neuromuscular complications of AIDS and certain metabolic muscle diseases. Combined clinical data, genetic information, HLA and MLC typing and studies of virus serology and virus isolation are performed. A neuromuscular disease that occurs in patients who have had poliomyelitis at an early age has been clinically defined; the rate of progression of post-polio weakness was defined and its clinical electrophysiological, virological and histochemical similarities with ALS were explored. The nature of oligoclonal bands found in the CSF of patients with post-polio and other chronic neurological diseases is under investigation. Patients with polymyositis are studied and a viral mechanism is being investigated; the muscle changes in these patients before and after a randomized double-blind controlled study with cyclophosphamide, plasmapheresis or lymphocytophoresis are being investigated. The clinical, electrophysiological and immunological picture of a chronic, sensory, "ataxic" neuropathy were defined and the presence of a ganglionopathy was found; the pathogenetic mechanisms of this neuropathy were also studied and the role of proprioceptive afferent inputs for their postural maintenance was defined. The metabolic activity of the cortex in ALS patients was studied using the PET scan and 18F 2-deoxy-D-glucose; hypometabolism was demonstrated not only in the motor but throughout the cortex, suggesting that ALS is a generalized process affecting many cortical regions. An experimental therapeutic trial with recombinant DNA alpha 2 human interferon was also in ALS patients. Muscle biopsies from patients with nephropathic cystinosis and renal Fanconi syndrome were studied morphologically and biochemically. Signs of a metabolic lipid storage myopathy due to carnitine deficiency were found; this promoted us to start a therapeutic study with carnitine replacement.